Essential oil in cats: we recommend not using the products on cats because cats have trouble detoxifying ‘phytoalexins’ and ‘phenolic’ like substances found in nature. Herein lies the controversy over which substances in plants and flowers, and how much, could tax or harm a cat’s liver. And since these substances in essential oils are hundreds of times more concentrated than in fresh flowers and plants, we seriously advise people not to use essential oils on cats unless under the care of a knowledgeable vet.